The present invention relates generally to power system communications, and more particularly to apparatus capable of simultaneously transmitting and receiving digital data signals both at high rates and over long distances through power lines and power line transformers, including AC, DC, coaxial cables, and twisted pair lines.
xe2x80x9cPower-line Carriersxe2x80x9d are well known in the field of power system communications. The principal elements of such power-line carriers are transmitting and receiving terminals, which include one or more line traps, one or more coupling capacitors, and tuning and coupling equipment. Detailed information regarding the description and typical composition of conventional power-line carriers may be found in Fundamentals Handbook of Electrical and Computer Engineering Volume II: Communication Control Devices and Systems, John Wiley and Sons, 1983, pp 617-627, the contents of which are incorporated herein by reference. A significant problem associated with prior art power-line carriers is their requirement for one or more line traps, one or more capacitors, one or more coupling transformers or carrier frequency hybrid circuits and frequency connection cables.
All traditional couplers incorporate a ferrite or iron core transformer which causes signal distortion due to the non-linear phase characteristic of the transfer function between the transmit coupler and the receive coupler. The distortion is created by the presence of magnetic core material which exhibits hysteresis. For distribution power-line carriers, the distortion is particularly severe because the signal must propagate through at least three such non-linear devices, the distribution transformer and two power-line couplers, that use ferrite core transformers. The distortion caused by these non-linear devices leads to envelope delay distortion, which limits communication speeds.
The major shortcoming of previous designs resulted from the use of ferrite or iron core transformers in the signal couplers. The primary winding inductance, L1, is altered to some unknown value due to the non-linearity of the core. This results in a mistuning of the desired carrier frequency. Also, the impedance of the primary winding at the desired carrier frequency is no longer matching the power line characteristic impedance. In recognition of this fact, other designs attempt to merely couple a signal onto a power line with a low transceiver input impedance by using a large coupling capacitor (approx. 0.5 uF). This results in a significant coupling loss of up to 20 dB at the carrier frequency.
My co-pending U.S. patent application Ser. No. 09/344,258 (xe2x80x9cthe ""258 Applicationxe2x80x9d) discloses a novel phase shift linear power, phone, twisted pair, and coaxial line coupler for both transmission and reception. The phase shift linear coupler comprises a novel air-core or dielectric core transformer which can be used for phone line, coaxial, LAN and power line communication through power line transformers. The phase shift linear coupler further comprises an associated coupling capacitor network in order to achieve resistive matching to approximately the lowest known value of the line characteristic impedance and to maximize stable signal transmission onto the line. This resonance effectively creates a band pass filter at carrier frequency. The disclosure of the ""258 Application is incorporated herein by reference in its entirety.
The designs of the ""258 Application solved many of the problems of previous designs, which used ferrite or iron couplers that resonated with the power line characteristic impedance, resulting in notches, suck outs and non-linear media for communications over various lines such as power lines. The phase shift linear coupler of the ""258 Application does not have notches at the communications bandwidth, allowing linear communication over a very wide range of frequencies.
There is still a need, however, for a power line communications system capable of simultaneously transmitting and receiving digital data signals using higher frequencies (e.g., 200 Mhz-500 GHz), thereby permitting communication at high rates using wide bandwidths and over long distances through power lines and power line transformers, including AC, DC, coaxial cables, and twisted pair lines.
Briefly stated, in a first embodiment, the present invention is a communications apparatus for communicating electrical signals through one or more electrical lines having a characteristic impedance. The communications apparatus comprises:
a modulator which modulates the electrical signals to produce a modulated carrier signal having a preselected frequency greater than or equal to 200 MHz;
a transmitter electrically connected to the modulator and having an output impedance, the transmitter transmitting the modulated carrier signal; and
a coupler connected between the electrical line and the transmitter, the coupler matching the output impedance of the transmitter means to the characteristic impedance of the electrical line and communicating the modulated carrier signal to the electrical line without substantial phase distortion.
In a second embodiment, the present invention is a communications apparatus for communicating electric signals through one or more electric lines having a characteristic impedance comprising:
a modulator which modulates the electric signals to produce a modulated carrier signal having a first preselected frequency greater than or equal to 200 Mhz;
a transmitter electrically connected to the modulator and having an output impedance, said transmitter transmitting the modulated carrier signal;
a first coupler connected between the electric line and the transmitter, said coupler matching the output impedance of the transmitter to the characteristic impedance of the electric line and communicating the modulated carrier signal to the electric line without substantial phase distortion;
a receiver having an input impedance, said receiver receiving the modulated carrier signal;
a demodulator electrically connected to the receiver, said demodulator producing a demodulated carrier signal having a second preselected frequency greater than or equal to 200 Mhz by demodulating the modulated carrier signal; and
a second coupler connected between the electric line and the receiver for matching the input impedance of the receiver to the characteristic impedance of the electric line and communicating the modulated carrier signal to the receiver without significant phase distortion.
In a third embodiment, the present invention is a communications apparatus for communicating electric signals through one or more electric lines having a characteristic impedance comprising:
a first modem which produces a first modulated carrier signal having a first preselected frequency greater than or equal to 200 MHz and demodulates a second modulated carrier signal having a second preselected frequency greater than or equal to 200 MHz;
a first transmitter having an output impedance, said transmitter connected to the first modem and transmitting the first modulated carrier signal;
a first receiver having an input impedance, said receiver connected to the first modem and receiving the second modulated carrier signal;
a first coupler connected between the electric lines and the first transmitter and the first receiver, said first coupler matching the output impedance of the first transmitter and the input impedance of the first receiver to the characteristic impedance of the electric lines and communicating the first and second modulated carrier signals without substantial phase distortion;
a second modem which produces the second modulated carrier signal and demodulates the first modulated carrier signal;
a second transmitter having an output impedance, said transmitter connected to the second modem and transmitting the second modulated carrier signal;
a second receiver having an input impedance, said receiver connected to the second modem and receiving the first modulated carrier signal; and
a second coupler connected between the electric lines and the second transmitter and the second receiver, said second coupler matching the output impedance of the second transmitter and the input impedance of the second receiver to the characteristic impedance of the electric lines and communicating the first and second modulated carrier signals without substantial phase distortion.